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How the snowshoe hare is losing its white winter coat

Like the iconic arctic fox, the snowshoe hare dons white fur for the winter—a good camouflage in the snow. But as the climate warms, the hares are increasingly ditching their winter wardrobes and keeping the brown fur they sport during the rest of the year. Now, a new study shows how: by borrowing a gene from a jackrabbit, one of their long-eared cousins.

To find out how snowshoe hares (Lepus americanus) maintain their summertime pelage, scientists sequenced the genomes of “winter white” and “winter brown” hares and compared them with the genomes of several relatives, including the black-tailed jackrabbit (L. californicus). They quickly realized that the black-tailed jackrabbit, which doesn’t undergo a winter wardrobe switch, must have mated multiple times with the winter browns. One key souvenir from that mating: a jackrabbit version of agouti, the gene that normally revs up its activity and turns snowshoe fur white in the winter, the researchers report today in Science. Hares carrying this borrowed gene are unable to turn white.

The finding is one of many suggesting hybridization is much more common than most scientists thought; by speeding up evolution, such interbreeding makes it possible for offspring to thrive under different conditions. That’s good news for snowshoe hares, the scientists say: As the climate warms, ever-larger regions will be snowless, making the white fur an ever-greater liability.